Conventional images are prepared from imagewise exposed photographic silver halide materials by subjecting them to one or more photographic processing solutions that include the various photochemical components necessary for providing a black-and-white and/or color image. At the very least, such materials require photochemical processing in a developer (to "develop" a silver image from exposed silver halide grains) and a fixer (to "fix" and remove unexposed silver halide). Color photographic processing requires additional steps in order to provide an acceptable dye image, for example a silver bleaching step between color development and fixing.
The various chemical formulations used in conventional photoprocessing steps have been prepared in both liquid and solid form. Many of the necessary photochemical components are already in solid form, and in early years of photography, solid processing compositions were common. However, it was often difficult to mix the solid components in a uniform fashion, and long mixing times were often then required for preparing aqueous working strength solutions. In addition, some of the photochemical components were reactive with each other, and could not be kept together without severe losses in activity, providing evidence of poor shelf life or stability.
More recently, commercial compositions have been prepared, shipped and used as aqueous solutions. Sometimes, they are provided in concentrated form in order to minimize costs associated with weight and volume, but they then require dilution upon use.
Even though concentrates provide some advantage in economy, they are usually storable for only a limited period of time, and the reduced amounts of solvent contained therein still increases shipping and storage costs. Thus, the photographic industry has long sought ways to provide stable photoprocessing formulations in dry form. Various manufacturers have developed powders, granules, solid tablets and other dry forms in recent years in response to these needs.
To date, solid compositions have not been widely accepted in the trade. One reason is that fine powdered compositions pose health risks to workers trying to formulate working solutions when the fine dust becomes airborne in the workplace. In addition, powdered chemicals are difficult to mix uniformly and consistently on a small scale, for example, in smaller photoprocessing labs. To achieve high uniformity, high energy mixing is required, and many photoprocessing customers cannot afford the needed mixing equipment or space. As the powders are made more fine, the dust problem increases and solubilization becomes more difficult.
In response to these problems, various means have been used in the industry to make powdered or granulated photochemicals, for example, fluidized bed agglomerators (see U.S. Pat. No. 4,923,786 of Kuhnert et al), extrusion processes (see U.S. Pat. No. 3,981,732 of Emoto et al), and freeze drying (U.S. Pat. No. 4,816,384 of Fruge et al).
Solid tablet chemistries have also been developed in the industry (see for example, U.S. Pat. No. 5,316,898 of Ueda et al), but the tablets lack widespread acceptance because they are more expensive than conventional photochemical compositions.
Clearly, there is a need in the art for dry, uniformly mixed photoprocessing compositions that are affordable, easy and safe to use, and readily prepared using readily available equipment and procedures. This invention is directed to solving these problems and meeting these needs.